An induction cooking hob including a cooking area with three or more induction coils and a method for controlling a cooking area

ABSTRACT

The present invention relates to an induction cooking hob ( 10 ) including at least one cooking area ( 12 ), wherein the cooking area ( 12 ) comprises at least three induction coils ( 14 ). The induction coils ( 14 ) of at least one cooking area ( 12 ) are arranged side-by-side and in series. Each induction coil ( 14 ) of at least one cooking area ( 12 ) has an elongated shape. The longitudinal axes of the induction coils ( 14 ) within one cooking area ( 12 ) are arranged in parallel. Each induction coil ( 14 ) of  10  the cooking area ( 12 ) is associated with a dedicated induction generator ( 16 ). The induction generators ( 16 ) are connected or connectable to at least one current line ( 18 ). The induction generators ( 16 ) are connected to and controlled or controllable by at least one control unit ( 20 ). Requested powers (rP) for each used induction generator ( 16 ) are adjusted or adjustable independent from each other by a user interface ( 22 ). Instant powers (iP) of the induction generators ( 16 ) within a cycle pattern (T1, T2, . . . , T11) are controlled or controllable independent from each other by the control unit ( 20 ). Further, the present invention relates to a method for controlling a cooking area.

The present invention relates to an induction cooking hob including atleast one cooking area comprises at least three induction coils.Further, the present invention relates to a method for controlling acooking area.

On cooking hobs, in particular on induction cooking hobs, there is apresent trend that the cooking zones are not arranged in fixed places,but are flexibly put together by one or more heating elements. Cookwaremay be put onto an arbitrary position of the cooking area by the user. Apot detection device recognizes said position, so that the heatingelements below the cookware may be activated.

However, it is difficult to set the appropriate powers for the relevantheating elements. Further, audible interference may be generate, if thedifference between the instant powers of adjacent activated inductioncoils corresponds with differences between frequencies within the rangeof audible interference.

It is an object of the present invention to provide an improvedinduction cooking hob with a cooking area and an improved method forcontrolling the power of the induction coils of the cooking area.

The object of the present invention is achieved by the induction cookinghob according to claim 1.

The induction cooking hob according to the present invention includes atleast one cooking area, wherein:

-   -   the cooking area comprises at least three induction coils,    -   the induction coils of at least one cooking area are arranged        side-by-side,    -   each induction coil of at least one cooking area has an        elongated shape,    -   the longitudinal axes of the induction coils within one cooking        area are arranged in parallel,    -   each induction coil of the cooking area is associated with a        dedicated induction generator,    -   the induction generators are connected or connectable to at        least one current line,    -   the induction generators are connected to and controlled or        controllable by at least one control unit,    -   requested powers for each used induction generator are adjusted        or adjustable independent from each other by a user interface,        and    -   instant powers of the induction generators within a cycle        pattern are controlled or controllable independent from each        other by the control unit.

The main idea of the present invention is the geometric properties ofthe cooking area and the induction coils on the one hand and thededicated induction generator for each induction coil of the cookingarea on the other hand. The geometric properties of the cooking area andthe induction coils allow a number of arrangements of cookware withdifferent shapes. The dedicated induction generator for each inductioncoil allows an independent setting of power of each induction coil.

Preferably, the induction coils of at least one cooking area have anoval and/or elliptical shape.

For example, the induction generators are connected or connectable tothe same current line.

Alternatively, the induction generators are connected or connectable toat least two different current lines, wherein said current lines havedifferent phases.

Further, the control unit may be provided for performing at least onecooking mode, wherein the activated induction coils work with one singlesetting of the requested power.

Moreover, the control unit may be provided for performing at least onecooking mode with at least two different settings of requested powers,wherein at least one activated induction coil works with the setting ofone requested power and at least one other activated induction coilworks with the setting of another requested power.

In particular, the cooking area comprises four induction coils.

Furthermore, the induction cooking hob may comprise a number of potdetection devices, wherein each induction coil is associated to at leastone pot detection device.

The object of the present invention is further achieved by the methodaccording to claim 9.

According to the present invention, the method is provided forcontrolling a cooking area on an induction cooking hob, wherein thecooking area comprises at least three induction coils and said methodcomprises the steps of:

-   -   setting a requested power for each used induction coil by a user        interface,    -   selecting a number of subsequent cycle patterns from a table        stored in a memory of a control unit,    -   defining activated and deactivated induction coils by each        selected cycle pattern,    -   determining a cycle time for each selected cycle pattern and a        power balance between the activated induction coils, so that a        desired average power for each induction coil is obtained over a        period of one or more selected cycle patterns, and    -   the sum of the instant powers of the activated induction coils        within each selected cycle pattern is equal to the sum of the        requested powers for each used induction coil.

Preferably, the difference between the instant powers of adjacentactivated induction coils is small enough, so that the differencebetween frequencies associated to the instant powers avoids thegeneration of audible interference. In particular, the differencebetween said frequencies is less than 1000 Hz.

Further, the desired average power for each induction coil over theperiod of one or more selected cycle patterns may be equal to therequested power for said induction coil.

Preferably, as many induction coils as possible are activated within onecycle patterns.

In a similar way, the instant powers of the activated induction coilsmay be as low as possible.

In particular, variations of the instant powers of the activatedinduction coils are as low as possible.

At last, the method is provided for the induction cooking hob mentionedabove. Novel and inventive features of the present invention are setforth in the appended claims.

The present invention will be described in further detail with referenceto the accompanied drawings, in which

FIG. 1 illustrates a schematic circuit diagram of a cooking area for aninduction cooking hob according to a preferred embodiment of the presentinvention,

FIG. 2 illustrates a schematic top view of the induction cooking hobaccording to the preferred embodiment of the present invention, and

FIG. 3 illustrates a further schematic top view of the induction cookinghob according to the preferred embodiment of the present invention.

FIG. 1 illustrates a schematic circuit diagram of a cooking area 12 foran induction cooking hob 10 according to a preferred embodiment of thepresent invention.

The cooking area 12 comprises four induction coils 14 arranged side-byside. In this example, the four induction coils 14 form a line. A first,second, third and fourth induction coil 14 is denoted by the letter A,B, C and D, respectively. Further, the cooking area 12 comprises fourinduction generators 16, a current line 18, a control unit 20 and a userinterface 22. The current line 18 is provided for supplying rectifiedmains voltage. The current line 18 is connected to power input terminalsof the four induction generators 16. Each induction generator 16corresponds with one induction coil 14. An output terminal of eachinduction generator 16 is connected to the associated induction coil 14.The user interface 22 is connected to an input terminal of the controlunit 20. Four output terminals of the control unit 20 are connected tocorresponding control input terminals of the induction generators 16.For example, the induction generator 16 is realized by a half-bridgeinverter. Each induction coil 14 is associated to at least one potdetection device.

By operating the user interface 22 different cooking modes can beselected by a user. For example, the user interface 22 may comprisededicated touch keys for said cooking modes. In a preferred embodimentthe following four cooking modes are provided. According to a firstcooking mode, the four induction coils A, B, C and D work with onesingle power setting. According to a second cooking mode, the fourinduction coils A, B, C and D work with two different power settings,wherein the first and second induction coils A and B work with one powersetting and the third and fourth induction coils C and D work withanother power setting. According to a third cooking mode, the fourinduction coils A, B, C and D work with two different power settings,wherein the first induction coil A works with one power setting and thesecond, third and fourth induction coils B, C and D work with anotherpower setting. According to a fourth cooking mode, the four inductioncoils A, B, C and D work with two different power settings, wherein thefirst, second and third induction coils A, B and C work with one powersetting and the fourth induction coil D works with another powersetting. The third and fourth cooking modes are the same in view of afunctional aspect.

In the first cooking mode, the induction coils 14 covered by cookwareare activated at the same working frequency in order to cancel acousticinterference noise. However, in the second, third and fourth cookingmodes, the induction coils 14 are affected by different power settingsand therefore by different frequencies, so that acoustic interferencenoise has to be avoided. The acoustic interference noise occurs, if thefrequency difference between adjacent induction coils 14 is within theaudible range of the human ear. Since the power is set by the user, thefrequency depends on the power setting, so that often the frequencydifference may be within the audible range.

In order to avoid the acoustic interference noise, the induction coils14 are activated and deactivated according to a number of subsequentcycle patterns T1 to T11, in which not all of the induction coils 14 areactivated during the same time. The sum of the instant powers iP of theactivated induction coils 14 is kept in such a way that the differencesof the instant powers iP between the cycle patterns T1 to T11 are small.In general, the variance of the instant powers iP must be small enoughin order to comply with existing norms for flickering on the currentline 18. The used cycle patterns T1 to T11 are structured in such a waythat adjacent activated induction coils 14 have a small or no frequencydifference. In contrast, the activated induction coils 14, which are notadjacent, may have different frequencies and powers.

The induction coils 14 activated at a certain time should have a totalinstant power iP, which is equal to the sum of all requested powers rP.However, a variation of the total instant power iP between the cyclepatterns T1 to T11 may be allowed with the scope of the EMC norms.

The following table illustrates the possible combinations of activatedand deactivated induction coils A, B, C and D, in which two, three orfour of the induction coils A, B, C and D are activated at the sametime. The first induction coil A is adjacent to the second inductioncoil B, in turn the second induction coil B is adjacent to the thirdinduction coil C, and the third induction coil C is adjacent to thefourth induction coil D, as shown in FIG. 1. The second line to thefifth line of said table indicate the activated and deactivated statesof the induction coils A, B, C and D, respectively. The eleven differentcycle patterns are denoted by T1 to T11 in the first line. The last lineof the table indicates the number N of the simultaneously activatedinduction coils A, B, C and D.

T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 A x x x x X x x B x x x x x x X C x xx x X x X D x x x x x x x N 4 3 3 3 3 2 2 2 2 2 2

A number of the cycle patterns T1 to T11 is selected from the abovetable. A relative cycle time t for each selected cycle pattern T1 to T11and a power balance between the induction coils A, B, C and D is set insuch a way, that the desired average power for each induction coil A, B,C and D is achieved over one or more cycle patterns T1 to T11. Theinstant power iP of the individual induction coils A, B, C and D dependson the number of activated induction coils A, B, C and D, the selectedpower balance and the total requested power rP. It is preferred, that asmany induction coils A, B, C and D as possible are activated within thegiven cycle pattern T1 to T11, so that the variation of the instantpowers iP of the induction coils A, B, C and D are minimized, and thatthe power is uniform.

The following table illustrates the default individual duty settings ofthe induction coils A, B, C and D for each cycle pattern T1 to T11. Thenumerical values in the second line to the fifth line of said tableindicate the percentages of the power of the induction coils A, B, C andD, respectively. The last line of the table indicates the number N ofthe simultaneously activated induction coils A, B, C and D.

T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 A 0.25 0.33 0.33 0.33 0.5 0.5 0.5 B0.25 0.33 0.33 0.33 0.5 0.5 0.5 C 0.25 0.33 0.33 0.33 0.5 0.5 0.5 D 0.250.33 0.33 0.33 0.5 0.5 0.5 N 4 3 3 3 3 2 2 2 2 2 2

In particular, the cycle patterns T6, T7 and T11 can be selected as thepreferred last cycle patterns, wherein the power balance between twoactivated induction coils A, B, C and/or D can be adjusted in order toachieve the desired power distributions. The activated induction coilsA, B, C and/or D of the cycle patterns T6, T7 and T11 are not adjacent.Thus, the activated induction coils A, B, C and/or D of the cyclepatterns T6, T7 and

T11 may have arbitrary frequencies without generating acousticinterference noise.

According to a first example, the requested power rP for the firstinduction coil A is rP=100 W, for the second induction coil B is rP=150W, for the third induction coil C is rP=350 W, and for the fourthinduction coil D is rP=400 W.

In said first example, the method of selecting the cycle patterns andsetting the duty are performed as follows. A cycle pattern with threeactivated induction coils B, C and D is selected, wherein the inductioncoil A is omitted, which has a requested power rP closest to thedifference between the highest and second highest requested power rP. Afurther cycle pattern is selected with two activated induction coils Cand D having the highest and second highest requested power rP until thepower is reach for the second highest power. Another cycle pattern isselected with two activated induction coils A and D having the highestrequested power iP and the biggest distance from each other. The powerbalance of the activated induction coils A and D is adjusted in order toreach the requested power rP. Thus, the cycle patterns T5, T9 and T11are selected.

The relative cycle time t of the cycle pattern T5 is calculated in sucha way, that the lowest requested power rP of the activated inductioncoils B, C or D is reached. This is the requested power rP=150 W for thesecond induction coil B. Further, the sum of the instant powers iP ofthe activated induction coils B, C and D is equal to the sum of therequested powers rP for the induction coils A, B, C and D, which isrP=1000 W. The relative cycle time t of the cycle pattern T5 is givenby:

t(T5)=iP(B)/(rP(A,B,C,D)/3)=150 W/(1000 W/3)=0.45

The relative cycle time t of the cycle pattern T9 is calculated in sucha way, that the instant power iP of the third induction coil C duringthe cycle pattern T5 is reached. Said instant power iP of the thirdinduction coil C during the cycle pattern T5 is given by:

iP(C;T5)=(rP(A,B,C,D)/3)*t(T5)=(1000 W/3)*0.45=150 W

In the cycle pattern T9 there are two activated induction coils C and D,so that the instant power iP of each activated induction coil C and D isgiven by:

iP(C)=iP(D)=rP(A,B,C,D)/2=1000 W/2=500 W.

The remaining power of the third induction coil C during the cyclepattern T9 is given by:

iP(C;T9)=rP(C)−iP(C;T5)*t(T5)=200 W

The relative cycle time t of the cycle pattern T9 is given by:

t(T9)=iP(C;T9)/(rP(A,B,C,D)/2)=200 W/(1000 W/2)=0.4

The relative cycle time t of the cycle pattern T11 is given as theremaining time.

t(T11)=1−t(T5)−t(T9)=1−0.45−0.40=0.15

Since the two remaining activated induction coils A and D are notadjacent, the power balance of said two induction coils A and D can bearbitrarily adjusted in order to obtain the desired power for bothinduction coils A and D. The instant powers iP of the activatedinduction coil A and D are given by

iP(A;T11)=rP(A)/t(T11)=100 W/0.15=666.7 W

iP(D;T11)=1−iP(A;T11)=333.3 W

The actual power aP of the fourth induction coil can be verified by:

aP(D)=1000 W*(0.45/3+0.4/2)+333.3 W*0.15=400 W

The following table illustrates the relative cycle times t, the instantpowers iP, the actual powers aP and the requested powers rP of the cyclepatterns T1 to T11 according to the first example.

T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 aP rP t 0 0 0 0 0.45 0 0 0 0.40 00.15 iP(A) 0 0 666.7 100 100 iP(B) 333 0 0 150 150 iP(C) 333 500 0 350350 iP(D) 333 500 333.3 400 400 Sum 1000 1000 1000 1000 1000

According to a second example, the cooking zones associated to thesecond, third and fourth induction coils B, C and D are always linked.In the second example, other combinations of cycle patterns are used.

FIG. 2 illustrates a schematic top view of the induction cooking hob 10according to the preferred embodiment of the present invention. A smallcooking vessel 28 and a big cooking vessel 30 are arranged on theinduction cooking hob 10. FIG. 2 relates to the second example.

The induction cooking hob 10 comprises a cooking area 12 including thefour induction coils 14 arranged in series. Moreover, the inductioncooking hob 10 comprises two further induction coils 24 and 26. The fourinduction coils 14 are elliptical, while the further induction coils 24and 26 are circular. The longitudinal axes of the four induction coils14 are arranged in parallel. The small cooking vessel 28 is arrangedabove the first induction coil A, while the big cooking vessel 30 isarranged above the second, third and fourth induction coils B, C and D.The positions of the small cooking vessel 28 and the big cooking vessel30 relates to the second example.

The second example differs between two cases. In a first case the powersetting of the first induction coil A is lower than the individualrequested powers rP of the other induction coils B, C and D, while in asecond case the power setting of the first induction coil A is higherthan the individual requested powers rP of the other induction coils B,C and D.

In the first case the cycle patterns T1 and T5 are applied. The cyclepattern T1 is applied until the requested power for the first inductioncoil A is reached, while the cycle pattern T5 is applied during the restof the time.

The sum of the instant powers iP of all activated induction coils A, B,C and/or D is always equal to the sum of the requested powers rP. In thecycle pattern T1 there are four activated induction coils A, B, C and D,so that the instant powers of each induction coil A, B, C and D is aquarter of the sum of the requested powers. The sum of the requestedpowers rP is:

rP(A,B,C,D)=100 W+300 W+300 W+300 W=1000 W

The relative cycle time t of the cycle pattern T1 is given by:

t(T1)=iP(A)/(rP(A,B,C,D)/4)=100 W/(1000 W/4)=0.4

The remaining relative cycle time t of the cycle pattern T5 is given by:

t(T5)=1−t(T1)=1−0.4=0.6

The following table illustrates the relative cycle times t, the instantpowers iP, the actual power aP and the requested powers rP of the cyclepatterns T1 to T11 according to the first case of the second example.

T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 aP rP t 0.4 0 0 0 0.6 0 0 0 0 0 0 1iP(A) 250 100 100 iP(B) 250 333.3 300 300 iP(C) 250 333.3 300 300 iP(D)250 333.3 300 300 Sum 1000 1000 1000 1000

In the second case the power setting of the first induction coil A ishigher than the individual requested powers rP of the other inductioncoils B, C and D.

In the second case the cycle patterns T2 and T11 are applied. The cyclepattern T2 is applied until the requested powers for the second andthird induction coils B and C are reached. In the cycle pattern T11 theinstant powers of the first and fourth induction coils A and D arematched in order to obtain the requested powers for said first andfourth induction coils A and D.

The sum of the instant powers iP is always equal to the sum of therequested powers rP. In the cycle pattern T2 there are three activatedinduction coils A, B and C, so that the instant power of each inductioncoil A, B and C is a third of the sum of the requested powers. The sumof the requested powers rP is:

rP(A,B,C,D)=300 W+100 W+100 W+100 W=600 W

The instant power iP of each induction coil A, B and C during the cyclepattern T2 is

iP(A)=iP(B)=iP(C)=rP(A,B,C,D)/3=200 W

The relative cycle time t of the cycle pattern T2 is given by:

t(T2)=rP(B)/(rP(A,B,C,D)/3)=100 W/(600 W/3)=0.5

The remaining relative cycle time t of the cycle pattern T11 is givenby:

t(T11)=1−t(T2)=1−0.5=0.5

Since the two remaining activated induction coils A and D are notadjacent, the power balance of said two induction coils A and D can bearbitrarily adjusted in order to obtain the desired power for bothinduction coils A and D.

The instant powers iP of the activated induction coil A and D are givenby

iP(D;T11)=rP(D)/t(T11)=100 W/0.5=200 W

iP(A;T11)=rP(A,B,C,D)−iP(D;T11)=600 W −200 W=400 W

The actual power aP of the first induction coil A can be verified by:

aP(A)=(600 W*0.5)/3+(400 W*0.5)=300 W

The following table illustrates the relative cycle times t, the instantpowers iP, the actual powers aP and the requested powers rP of the cyclepatterns T1 to T11 according to the second case of the second example.

T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 aP rP t 0 0.5 0 0 0 0 0 0 0 0 0.5 1iP(A) 200 400 300 300 iP(B) 200 100 100 iP(C) 200 100 100 iP(D) 200 100100 Sum 600 600 600 600

FIG. 3 illustrates a further schematic top view of the induction cookinghob according to the preferred embodiment of the present invention. Twomedium cooking vessels 32 and 34 are arranged on the induction cookinghob 10. FIG. 3 relates to an example with two current lines on differentphases.

The induction cooking hob 10 comprises the cooking area 12 including thefour induction coils 14 arranged in series. Additionally, the inductioncooking hob 10 comprises the two further induction coils 24 and 26. Thefour induction coils 14 are elliptical, while the further inductioncoils 24 and 26 are circular. The longitudinal axes of the fourinduction coils 14 are arranged in parallel. A first medium cookingvessel 32 is arranged above the first induction coil A and the secondinduction coil B, while a second medium cooking vessel 34 is arrangedabove the third induction coil C and the fourth induction coil D. Thefirst induction coil A and the second induction coil B are supplied by afirst current line, while the third induction coil C and the fourthinduction coil D are supplied by a second current line, wherein thefirst and second current lines are on different phases.

In order to avoid the acoustic interference noise, the adjacentinduction coils A, B, C and/or D cannot be activated at the same timewith a frequency difference within the audible range. The sum of theinstant powers iP of the first and second induction coils A and B shouldbe constant. In a similar way, the sum of the instant powers iP of thethird and fourth induction coils C and D should also be constant.

The following table illustrates the possible cycle patterns T1 to T3.

T1 T2 T3 A x x B x x C x x D x x

The following table illustrates the relative cycle times t, the instantpowers iP, the actual powers aP and the requested powers rP of the cyclepatterns T1 to T3 according to an example, in which the first inductioncoil A and the second induction coil B are supplied by the first currentline, while the third induction coil C and the fourth induction coil Dare supplied by the second current line, wherein the first and secondcurrent lines are on different phases.

T1 T2 T3 aP rP t 0 0.5 0.5 iP(A) 350 980 0 490 500 iP(B) 350 0 980 490500 iP(C) 350 420 0 210 200 iP(D) 350 0 420 210 200 Sum 1400 1400 14001400

If the sum of the requested powers rP of the first induction coil A andthe second induction coil B is equal or about equal to the sum of therequested powers rP of the third induction coil C and the fourthinduction coil D, then the cycle pattern T1 is applied the full time.However, if the above requested powers are different, then the cyclepatterns T2 and T3 are applied, wherein the relative cycle time t is 0.5or 50%. The sum of the instant powers iP of the first induction coil Aand the second induction coil B is equal to the sum of the correspondingrequested powers rP. In a similar way, the sum of the instant powers iPof the third induction coil C and the fourth induction coil D is equalto the sum of the corresponding requested powers rP.

Another application of the present invention is the activation of afurther cooking mode, wherein the requested power (rP) changesautomatically according to the position of the cooking vessel on thecooking area. The system performs a pot detection on all coils in thecooking area. Depending on which coil or coils) that is (are) covered bythe cooking vessel, power is applied to the coil (coils) according to apreset pattern. The requested power (rP) can for instance be low, forexample about 400 W, if the cooking vessel is placed on one of theextreme parts of the cooking area. In contrast, the requested power (rP)can be high, for example about 3000 W, if the cooking vessel is placedon the other (opposite) extreme part of the cooking area. At last, therequested power (rP) can have an average value, if the cooking vessel isplaced on a central portion of the cooking area, between the extremeparts. A user could be allowed to change the preset pattern from theuser interface to obtain the best pattern for the cooking needs at everyinstance. Applied on the embodiment in FIG. 1, pair of coils could beutilised as the defining regions of preset power, e.g. if a vessel isplaced on coils A+B a high power is applied, if placed on coils B+C amedium power I applied and if placed on coils C+D a low power isapplied. Naturally, other combinations are possible. If a cooking vesselis moved or removed, a new pot detection can be performed to ensure thatonly the relevant coil or coils are actine.

LIST OF REFERENCE NUMERALS

-   10 induction cooking hob-   12 cooking area-   14 induction coil-   16 induction generator-   18 current line-   20 control unit-   22 user interface-   24 further induction coil-   26 further induction coil-   28 small cooking vessel-   30 big cooking vessel-   32 medium cooking vessel-   34 medium cooking vessel-   A first induction coil-   B second induction coil-   C third induction coil-   D fourth induction coil-   N number of activated inductions coils-   Tn cycle pattern-   t relative cycle time-   iP instant power-   aP actual power-   rP requested power

1. An induction cooking hob including at least one cooking area,wherein: the at least one cooking area comprises at least threeinduction coils, the induction coils of the at least one cooking areaare arranged side-by-side, each induction coil of the at least onecooking area has an elongated shape, the longitudinal axes of theinduction coils within the at least one cooking area are arranged inparallel, each induction coil of the at least one cooking area isassociated with a dedicated induction generator, the inductiongenerators are connected or connectable to at least one current line,the induction generators are connected to and controlled or controllableby at least one control unit, requested powers (rP) for each usedinduction generator are adjusted or adjustable independent from eachother by a user interface, and instant powers (iP) of the inductiongenerators within a cycle pattern (T1, T2, . . . , T11) are controlledor controllable independent from each other by the control unit.
 2. Theinduction cooking hob according to claim 1, characterized in that theinduction coils of the at least one cooking area have an oval and/orelliptical shape.
 3. The induction cooking hob according to claim 1,characterized in that the induction generators are connected orconnectable to the same current line.
 4. The induction cooking hobaccording to claim 1, characterized in that the induction generators areconnected or connectable to at least two different current lines,wherein said current lines have different phases.
 5. The inductioncooking hob according to claim 1, characterized in that the control unitis provided for performing at least one cooking mode, wherein theactivated induction coils work with one single setting of the requestedpower (rP).
 6. The induction cooking hob according to claim 1,characterized in that the control unit is provided for performing atleast one cooking mode with at least two different settings of requestedpowers (rP), wherein at least one activated induction coil works withthe setting of one requested power (rP) and at least one other activatedinduction coil works with the setting of another requested power (rP).7. The induction cooking hob according to claim 1, characterized in thatthe at least one cooking area comprises four induction coils.
 8. Theinduction cooking hob according to claim 1, characterized in that theinduction cooking hob comprises a number of pot detection devices,wherein each said induction coil is associated to at least one potdetection device.
 9. A method for controlling a cooking area on aninduction cooking hob, wherein the cooking area comprises at least threeinduction coils and said method comprises the steps of: setting arequested power (rP) for each used induction coil by a user interface,selecting a number of subsequent cycle patterns (T1, T2, . . . , T11)from a table stored in a memory of a control unit, defining activatedand deactivated induction coils by each selected cycle pattern (T1, T2,. . . , T11), determining a cycle time (t) for each selected cyclepattern (T1, T2, . . . , T11) and a power balance between the activatedinduction coils, so that a desired average power for each induction coilis obtained over a period of one or more selected cycle patterns (T1,T2, . . . , T11), and the sum of instant powers (iP) of the activatedinduction coils within each selected cycle pattern (T1, T2, . . . , T11)is equal to the sum of the requested powers (rP) for each used inductioncoil.
 10. The method according to claim 9, characterized in that thedifference between the instant powers (iP) of adjacent activatedinduction coils is small enough, so that the difference betweenfrequencies associated to the instant powers (iP) avoids the generationof audible interference.
 11. The method according to claim 9,characterized in that the desired average power for each induction coilover the period of one or more selected cycle patterns (T1, T2, . . . ,T11) is equal to the requested power (rP) for said induction coil. 12.The method according to claim 10, characterized in that as manyinduction coils as possible are activated within one cycle patterns (T1,T2, . . . , T11).
 13. The method according to claim 9, characterized inthat the instant powers (iP) of the activated induction coils are as lowas possible.
 14. The method according to claim 9, characterized in thatvariations of the instant powers (iP) of the activated induction coilsare as low as possible.
 15. The method according to claim 9,characterized in that the method is provided for the induction cookinghob according to claim 1.